A position control to move a table in longitudinal, traverse and circular directions is disclosed in Japanese Patent Laid-Open No. 99243/1996, which has three bearing units to allow a table moving relative to a stationary bed in any direction of X-, Y- and circular directions. Each bearing unit is composed of a pair of linear motion guide units that are each made up of a guide member and a moving member, which is jointed for rotation with another moving member of the counterpart. Any two bearing units lie in parallel relation with one another between the stationary bed and the table while the third one is arranged in perpendicular to the two bearing units. The bearing units are each provided with a linear moving mechanism composed of a ball screw, a lead nut and a motive source.
Another prior position control of biaxial linear-revolving guide means disclosed in Japanese Patent Laid-Open No. 245128/1999, which has biaxial linear guide means composed of a first guide rail and a second guide rail arranged in perpendicular to the first guide rail and connected with the first guide rail through a moving carriage, and a circular guide means made in the second guide rail. Some biaxial linear-revolving guide means recited earlier are disposed between a stationary bed and a table and associated with one another by any linear driving mechanism to form a biaxial linear-revolving table system. The circular guide means is provided therein with a crossed-roller bearing and associated with the second guide rail using any joint member. The biaxial linear-revolving guide means has any driving mechanism.
A prior table system disclosed in Japanese Patent Laid-Open No. 300557/1999 has a turning mechanism disposed between first and second carriages.
In Japanese Patent Laid-Open No. 93757/1996, moreover, there is disclosed a crossed-roller bearing composed of an inner ring, an outer ring surrounding the inner ring, and more than one roller installed between the inner and outer rings. Both the inner and outer rings are made on axially opposing ends thereof with threaded holes, which are used to fasten the bearing to any desired component including a housing, spindle and so on. The crossed-roller bearing, however, is envisaged to keep lubricant against any leakage through a plug while contain vibration that might be otherwise caused in the plug by rolling motion of the rollers. The outer ring is fastened to the stationary housing while the inner ring is bolted to the spindle. Nevertheless, the inner and outer rings have no construction to directly mount them to the slider of the linear motion guide unit.
Now referring to FIG. 25, there is shown an example of prior linear motion guide units commonly known to those skilled the art. The prior linear motion guide unit is mainly comprised of an elongated guide rail 72 and a slider 71 that fits over and conforms to the guide rail 72 for linear movement. The guide rail 72 is made on widthwise opposing sides thereof with lengthwise raceway grooves 73, one to each side. The slider 71 is allowed to move along the guide rail 72 in sliding way by virtue of rolling elements 79. The guide rail 72 is made on a lengthwise upper surface 74 thereof with holes 75 that are arranged lengthwise at a fixed interval. The guide rail 72 is fastened down to any mounting base such as a bed, machine bed, working bench, and so on with fastening bolts that extend through the holes 75 in the guide rail 72 to be screwed into the threaded holes in the mounting base. The slider 71 includes a carriage 76 made with raceway grooves 80 in opposition to the raceway grooves 73 on the guide rail 72, and end caps 77 secured to forward and aft ends of the carriage 76, one to each end. The carriage 76 is provided on an upper surface thereof with bolt holes 78 that are used to fasten any other appliance, machine component, chuck, clamping jaw, and so on to the slider 71. The rolling elements 79, as they roll, are allowed to recirculate through load races defined between the opposed raceway grooves 73, 80, turnaround races in the end caps 77 and return passages 81 extending in the carriage 76. Moreover, retainer bands 85 are attached to the carriage 76 to embrace the rolling elements 79 lest they fall away from the carriage 76. Also mounted on the end caps 77 are end seals 84, one to each end cap, for keeping sealing function between the guide rail 72 and the lengthwise opposing forward and aft ends of slider 71.
For the application of the linear motion guide unit to the table system where the table is allowed to move linearly in biaxial directions and also turn in circular direction as recited earlier, joining the moving member, or the slider, for revolving movement with one another is commonly done with just one shoulder bolt through the bearing. Such prior revolving joint, because of easy to be lopsided when having undergone any moment of load, is unsteady and, therefore, is not ready for the table system that needs precise position-control.
With the prior biaxial linear-revolving guide means in which the revolving guide means is secured to the table system through the joint member as stated earlier, the precise table system needs many components that are made with accuracy and very tough to assemble them into the table system. Besides, since the revolving guide means is rigidly connected to the second guide rail, any movement of the second guide rail results in entailing the simultaneous movement of the revolving guide, getting the center of the revolving guide means to move past away from the first guide rail into off-alignment where the table system would come into unsteady situation to get worse in precise position-control.
Further, the conventional table systems as stated earlier, because the revolving guide means fits through the joint member, is much tough to provide the table system that can make position control with highly accuracy.